Pfaff sewing machine mode 483-798/01, manufactured in the Federal Republic of Germany and distributed in the United States by Cohen Shoe Machinery Company, Inc. located at 35 Congress Street, Salem, Mass. 01970, is an example of a sewing machine that can form decorative stitches in a workpiece such as a shoe upper by reciprocating a needle and a presser foot in synchronism so that the needle penetrates the workpiece at spaced intervals and forms stitches in the workpiece and the presser foot engages the workpiece during its penetration by the needle to hold the workpiece stationary and rises upwardly of the workpiece to permit shifting of the workpiece relative to the needle between penetrations of the needle into the workpiece.
When the thickness of the workpiece varies, it has been found that a zone of reciprocation of the presser foot for a relatively thin workpiece portion that is satisfactory is unsatisfactory for a thicker workpiece portion. With the thinner workpiece portion, the presser foot in its lowermost position engages the workpiece top with sufficient pressure to prevent its shifting with a thicker workpiece portion and with the zone of reciprocation of the presser foot unchanged, it has been found that the presser foot penetrates the workpiece too deeply and either mars the workpiece, causes the resistance to penetration of the workpiece by the presser foot to damage the parts that effect the reciprocation of the presser foot, or adversely affects the timing of the motions of the needle and the presser foot to thereby adversely affect the quality of the stitches formed in the workpiece.